Defect detector for corrugated cardboard flutes

ABSTRACT

A defect detector for corrugated cardboard flutes comprises an optical projector for projecting to traveling flutes an inspection light having an effective line of which the length is about one pitch of flutes inclined slightly so that a tip of a normal flute is positioned on or slightly under the posterior end of the effective line and simultaneously a slope of an adjacent normal flute is positioned on the anterior end side of the effective line, an optical receiver equipped with a light-receiving element for receiving the inspection light reflected by a flute to output information according to the light-receiving position, and normal or abnormal determining means which determines that the flute height is normal if the light-receiving position detected is within an allowable range Wp.

This application is the national stage of International Application No.PCT/JP2007/073836, filed on Dec. 11, 2007.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to defect detectors for detecting whethercorrugated cardboard flutes (columns) are higher than or lower than anallowable range.

2. Description of Related Art

In the manufacture of corrugated cardboard sheets, at a step of forminga medium base paper into a corrugated shape and laminating thecorrugated medium to a liner, a defective portion such as a crushedflute mountain (flute crush), an inclined flute mountain (fluteinclination), or a projecting flute mountain (flute projection) causedby partial detachment of the corrugated medium from the liner or thelike may be generated, which results in unevenness in thickness of thecorrugated cardboard sheet. The present applicant has proposed a methodof detecting the occurrence of this above-described defect by means of amethod wherein flutes are examined on the manufacturing line duringproduction of cardboard sheets, rather than after production is complete(See Patent Document 1).

This method is a method in which “a limited distance sensor fordetecting that an object to be detected is positioned on an effectiveline of an inspection light is used, the effective line is set to alength approximately equal to one pitch of corrugated cardboard flutes,an inspection light is slightly inclined so that a tip of a normal flutemountain is positioned on or slightly under the posterior end of theeffective line and simultaneously a slope of an adjacent normal flutemountain is positioned on the anterior end side of the effective line,normalcy is detected from the fact that normal mountains of travelingflutes are constantly positioned on a part of the effective line,abnormality of a flute mountain higher than a standard flute height isdetected from the fact that a high flute mountain passes the inspectionlight on the sensor side outside the posterior end of the effectiveline, and abnormality of a flute mountain lower than the standard fluteheight is detected from the fact that a flute does not exist on theeffective line because a slope of a low mountain does not reach theanterior end of the effective line when the previous mountain ispositioned outside the posterior end of the effective line”.

Conventionally, the method has been realized by a detector including anoptical projector for projecting to traveling flutes an inspection lightinclined to graze a flute tip of a normally corrugated medium and reacha slope of an adjacent normal flute mountain thereto, and an opticalreceiver for detecting whether a light is received or not within alight-receiving range capable of receiving only the inspection lightreflected by a flute mountain on the effective line.

According to such a detector, when the heights of flute mountains arewithin the allowable range, the inspection light projected by theoptical projector is constantly reflected on the effective line and isreceived by the optical receiver. On the other hand, when the height ofany flute mountain is higher than the allowable range, the inspectionlight is reflected by the flute mountain outside the posterior end ofthe effective line, so the optical receiver does not receive theinspection light. Further, when the height of any mountain is too low toreach the allowable range, the inspection light is reflected by theflute mountain outside the anterior end of the effective line, so theoptical receiver does not receive the inspection light similarly.

Therefore, while the light is being detected by the optical receiver, itcan be determined that the height of a flute is within the allowablerange, and while the light is not detected by the optical receiver, itcan be detected that either defect (i.e., the height of a flute ishigher or lower than the allowable range) has been generated. That is,without requiring actual measurement of the height of a flute, whetherthe height of the flute is normal or not can be detected easily bydetecting whether the optical receiver receives the inspection light ornot.

[Patent Document 1] Japanese Patent No. 2571520

SUMMARY OF THE INVENTION Technical Problem

In such a detecting method as described above, in order to adjustdetection accuracy, in other words, in order to change the allowablerange of the flute height, it is required to change the length or theposition of the effective line. However, in order to change the lengthor the position of the effective line in the conventional detector, itis required to change the angle of the inspection light projected by theoptical projector, the position of the optical receiver, or the focusingangle of the reflected light, so that it is difficult to performadjustment.

Further, as a fluted medium of a corrugated cardboard material, there isa plurality of corrugation types such as “A” flute (the flute height isin a range of 4.5 to 4.8 mm), “B” flute (the flute height is in a rangeof 2.5 to 2.8 mm), and “C” flute (the flute height is in a range of 3.5to 3.8 mm), and if the corrugation types of corrugating mediums aredifferent, the lengths or positions of the effective lines are largelydifferent. Therefore, in the conventional detector in which it isdifficult to change the length or position of the effective line, it isdifficult to make use of the same detector to detect defects in flutesdifferent in corrugation type.

Additionally, in recent years, a corrugator which can replace acorrugating roll for forming a medium base paper into a corrugated shapeby another in a cassette manner, and can manufacture corrugatedcardboard sheets varying in corrugation type on the same manufacturingline has been widely spread. Therefore, a detector which can determinewhether or not the heights of flutes with a plurality of corrugationtypes are normal has been strongly desired.

The present invention provides, in view of the above circumstances, adefect detector for corrugated cardboard flutes, capable of easilyadjusting detection accuracy and detecting whether the heights of fluteswith a plurality of corrugation types are normal or not.

Solution to Problem

In order to solve the above problems, a defect detector for corrugatedcardboard flutes according to the present invention is “a defectdetector for corrugated cardboard flutes including an optical projectorwhich projects, to traveling flutes, an inspection light having aneffective line of which the length is about one pitch of flutes inclinedslightly so that a tip of a normal flute mountain is positioned on orslightly under the posterior end of the effective line andsimultaneously a slope of an adjacent normal flute mountain ispositioned on the anterior end side of the effective line, anddetermining whether the height of a flute is normal or abnormal basedupon the inspection light reflected by a flute mountain, comprising anoptical receiver equipped with a light-receiving element for receivingthe inspection light reflected by a flute mountain to output informationcorresponding to the light-receiving position, and normal or abnormaldetermining means for, if the light-receiving position detected from theinformation output by the light-receiving element is within an allowablerange, determining that the height of the flute is normal, and, if thelight-receiving position is out of the allowable range, determining thatthe height of the flute is abnormal”.

As the “optical projector”, a device may be used which projects lightusing a light-emitting element such as a light-emitting diode or a laserdiode.

As the “light-receiving element” for outputting “informationcorresponding to the light-receiving position”, for example, a PSD(position sensitive detector) element may be used. The PSD element is ahorizontally-long photoelectric element, provided with output terminalson both ends, current is output to both the output terminals when anelectric charge is generated by light reception. At this time, sinceresistance is proportional to a distance from the light-receivingposition to the output terminals, the light-receiving position can bedetected as a centroidal position of a light quantity based upon theratio of currents (or converted voltages) output from the two outputterminals. Therefore, when the PSD element is used as thelight-receiving element, the ratio of currents or voltages output fromthe two output terminals corresponds to “information corresponding tothe light-receiving position” in the present invention.

Alternatively, as the “light-receiving element for outputtinginformation according to a light-receiving position”, a plurality ofphotodiodes provided in array can be used, and in addition to thephotodiode array, a CMOS image sensor, a CCD image sensor, or the likecan be used. In this case, since the photodiode generating electriccharge by light reception can be specified by its output, thelight-receiving position can be detected as a position of the specifiedphotodiode. That is, in this case, the output from the photodiode whichhas received light and positional information (coordinates or the like)of the photodiode corresponding to “information corresponding to thelight-receiving position” in the present invention.

Incidentally, the “optical receiver” can be configured to include a lenswhich focuses reflected light from a flute mountain, an amplifier whichamplifies an output from the light-receiving element, and the like, inaddition to the light-receiving element.

The “normal or abnormal determining means” can be configured as aprogram for causing a computer to function. Alternatively, the “normalor abnormal determining means” can be configured using a comparator oran operational amplifying circuit which can compare an analog voltageoutput from the light-receiving element corresponding to thelight-receiving position and a voltage corresponding to the upper limitor the lower limit of the allowable range with each other.

According to the present invention, since the light-receiving positionof the inspection light reflected by a flute mountain can be specifiedowing to the above configuration, the “allowable range of the fluteheight” can be changed as an “allowable range of the light-receivingposition”. Thereby, without necessitating the changes of the angle ofthe inspection light, the position of the optical receiver, or the like,it becomes possible to adjust the detection accuracy easily by changingthe length or position of the effective line.

In addition, even when corrugated cardboard materials differing incorrugation type are manufactured on the same manufacturing line of thecorrugator, whether or not the height of a flute is normal can bedetermined by the same detector by shifting the allowable range of thelight-receiving position without demanding the changes of the angle ofthe inspection light, the position of the optical receiver, or the like.

The defect detector for corrugated cardboard flutes according to thepresent invention further comprises “a storage device which has storedan allowable range database associating flute type information includingcorrugation type information, medium information, and liner informationwith allowable range data, information acquiring means which acquiresthe flute type information from a production management device of thecorrugator, and allowable range shifting means for reading, from theallowable range database, the allowable range data associated with theflute type information acquired by the information acquiring means toshift the allowable range so as to conform the same to the readallowable range data”.

The “corrugation type information” can be a type of corrugation such as“A” flute, “B” flute, or “C” flute, or the number of flutes per unitlength. Further, as a “medium information”, the thickness of a mediumbase paper, basis weight, model number, and the like can be taken as anexample, and as a “liner information”, the thickness of a liner, basisweight, model number, and the like can be taken as an example.

The “allowable range data” can be described by a combination of theupper limit and the lower limit of the allowable range, and can be setbased upon calculation, actual measurement, or the like, by the flutetype information made of a combination of the corrugation typeinformation, the medium information, and the liner information or thelike.

As the “storage device”, an embedded memory of a computer, or anexternal storage device such as a hard disk, a flexible disk, or a CD-Rmay be used. Further, the “information acquiring means” and the“allowable range shifting means” can be realized as a function of acomputer, the processing of which is performed by a central processoraccording to a program stored in a main storage device.

If the basis weights (and thus the thickness) of a paper used as amedium base paper or a liner are different even if the corrugation typesare the same, the heights of flutes are different. Then, the productionmanagement device of the corrugator generally includes various kinds ofinformation related to corrugated cardboard sheets to be manufacturedsuch as corrugation types, combinations of a medium base paper and aliner to be attached with each other, respective model numbers of mediumbase papers or liners, respective basis weight of medium base papers orliners, and manufacturing order in a case of manufacturing plural kindsof corrugated cardboard sheets.

In the present invention, among these information items which areincluded by the production management device of the corrugator, theflute type information associated with the flute height is utilized.Thereby, the allowable range data suitable for normality determinationof the height of a flute of a corrugated cardboard sheet to bemanufactured is selected from the allowable range database, and whetheror not the height of a flute is normal can be determined more properly.

As above, as an effect of the present invention, it is possible toprovide a defect detector for corrugated cardboard flutes which canadjust the detection accuracy easily and can determine whether theheights of flutes with a plurality of corrugation types are normal ornot by the same detector.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is an explanatory diagram for explaining a detection principle ofa defect detector for corrugated cardboard flutes which is an embodimentof the present invention;

FIG. 2 is an explanatory diagram for explaining the detection principleof the defect detector for corrugated cardboard flutes;

FIG. 3 is an explanatory diagram for explaining the detection principleof the defect detector for corrugated cardboard flutes;

FIG. 4 is an explanatory diagram for explaining the detection principleof the defect detector for corrugated cardboard flutes;

FIG. 5 is a block diagram showing a configuration of the defect detectorfor corrugated cardboard flutes; and

FIG. 6 is a block diagram showing a functional configuration of thedefect detector for corrugated cardboard flutes in FIG. 5.

DETAILED DESCRIPTION OF THE INVENTION

Hereinafter, a defect detector for corrugated cardboard flutes which isa best mode of the present invention will be explained in reference toFIG. 1 to FIG. 6. Here, FIG. 1 to FIG. 4 are explanatory diagrams forexplaining a detection principle of the defect detector for corrugatedcardboard flutes which is an embodiment of the present invention, FIG. 5is a block diagram showing a configuration of the defect detector forcorrugated cardboard flutes, and FIG. 6 is a block diagram showing afunctional configuration of the defect detector for corrugated cardboardflutes in FIG. 5.

As shown in FIG. 1, a defect detector for corrugated cardboard flutes 1(hereinafter, “detector 1”) of the embodiment is a detector 1 whichincludes an optical projector 2 for projecting, to a traveling flutes,an inspection light 5 having an effective line 6 of which the length isabout one pitch of flutes inclined slightly so that a tip of a normalflute mountain 31 is positioned on or slightly under the posterior endof the effective line 6 and simultaneously a slope of an adjacent normalflute mountain 31 is positioned on the anterior end side of theeffective line 6, and determining whether the height of a flute isnormal or abnormal based upon the inspection light 5 reflected by aflute mountain, the detector 1 comprising an optical receiver 4 equippedwith a light-receiving element 4 a for receiving the inspection light 5reflected by a flute mountain to output information corresponding to thelight-receiving position. Incidentally, FIG. 1 illustrates a case inwhich the tip of the normal flute mountain 31 is positioned slightlybelow the posterior end of the effective line 6 and the anterior end ofthe effective line 6 is positioned slightly beyond the slope of thenormal flute mountain 31 adjacent thereto, and in this case, anallowable range of the flute height is Wh.

To explain the above in more detail, the optical projector 2 includes alight-emitting element 2 a, and projects the inspection light 5 from thelight-emitting element 2 a. Further, the optical receiver 4 includes aPSD element serving as the light-receiving element 4 a and a lens 4 bfocusing the reflected light. Further, the optical projector 2 and theoptical receiver 4 are disposed in the vicinity of a manufacturing linein the process of conveying a single-faced corrugated cardboard sheet 50formed by attaching a linerboard 40 on one side of a corrugated medium30 to a step of being laminated to another linerboard (not shown) on theother side. Further, the optical projector 2 and the optical receiverare provided with plural pairs at 50 mm to 100 mm intervals with respectto a width direction of the single-faced corrugated cardboard sheet 50.

Additionally, detector 1 of the present embodiment includes a computer60 connected to a production management device 90 of the corrugator bywire or wireless communication, as shown in FIG. 5. Here, computer 60includes a main storage device 62, a central processor 61 for performingprocessing according to a program stored in the main storage device 62,and an auxiliary storage unit 63. Here, the auxiliary storage unit 63 ofthe present embodiment corresponds to a storage device of the presentinvention.

Further, detector 1 includes an A/D converter 8 for digitally convertingan analog voltage output from optical receiver 4, and an abnormalityprocessor 91 for alarming abnormality with warning lamp, warning sound,or the like when a corrugated cardboard sheet with a defective fluteheight is generated, and eliminating the corrugated cardboard with adefective flute height from a manufacturing line based upon detection ofa conveying distance by an encoder.

A main functional configuration in detector 1 is a control mechanismunit 70 of the computer 60, and, as shown in FIG. 6, it includes anormal or abnormal determining means 71 which compares a light-receivingposition with an upper limit and a lower limit of an allowable range Wpbased upon a voltage output according to the light-receiving positionfrom the light-receiving element 4 a, and makes normal determination ifthe light-receiving position is within the allowable range Wp, or makesabnormal determination if the light-receiving position is out of theallowable range Wp.

Further, control mechanism unit 70 includes storing means 75 which hasstored an allowable range database 85 associating flute type information82 including corrugation type information, medium information, and linerinformation with allowable range data 86, information acquiring means 72which acquires production management information 81 including the flutetype information 82 from the production management device 90 of acorrugator, and allowable range shifting means 73 which reads theallowable range data 86 associated with the acquired flute typeinformation 82 from the allowable range database 85, and shifts theallowable range Wp so as to conform the same to the read allowable rangedata 86.

Next, the detection principle in detector 1 and the defects detectingmethod in detector 1 will be explained. First, a case in which a flutemountain 31 includes a normal height will be explained. As illustratedin FIG. 1, when an inspection light 5 is projected from light-emittingelement 2 a of optical projector 2 in a direction opposite to atravelling direction of a corrugated medium, inspection light 5 isreflected by flute mountain 31 with a normal height. After focused onthe light-receiving lens 4 b, reflected light 11 is received bylight-receiving element 4 a (PSD element), and a voltage is output fromterminals on both ends of light-receiving element 4 a by the ratiocorresponding to a light-receiving position 21. An analog voltage outputfrom the light-receiving element 4 a is input into the computer 60 afterdigitally converted by the A/D converter 8, and is compared with theupper limit and the lower limit of the allowable range Wp of thelight-receiving position corresponding to the allowable range Wh by thenormal or abnormal determining means 71. Then, since light-receivingposition 21 is within the allowable range Wp, it is determined that theheight of the flute is normal.

When the heights of flute mountains are within the allowable range Wh,as shown in FIG. 2, inspection light 5 is constantly reflected by aflute mountain on effective line 6, and light-receiving position 21 ofthe reflected light 11 is constantly positioned within the allowablerange Wp. To the contrary, as shown in FIG. 3, in a case of a flutemountain 32 which is high beyond the allowable range Wh, inspectionlight 5 is reflected outside effective line 6, and a light-receivingposition 22 of reflected light 12 is out of the allowable range Wp.Further, in a case of a flute mountain 33 which is too small to reachthe allowable range Wh, inspection light 5 is similarly reflectedoutside the effective line 6, a light-receiving position 23 of reflectedlight 13 is out of the allowable range Wp. Therefore, by detectingwhether or not a light-receiving position of reflected light is withinthe allowable range Wp, it can be known whether or not the height of theflute is within the allowable range Wh, so that determination can bemade about whether the height of the flute is normal or abnormal.

When it is determined by the normal or abnormal determining means 71that the height of the flute is abnormal, an abnormal signal 89 is sentfrom the normal or abnormal determining means 71 toward the abnormalityprocessor 91. Then, by the abnormality processor 91 receiving abnormalsignal 89, abnormal processing such as lighting-up of the warning lamp,actuation of warning sound buzzer, or elimination of a corrugatedcardboard with an abnormal flute height from the manufacturing line isperformed.

When a corrugation type of a flute to be inspected is changed, or wheninspection accuracy is wanted to be changed, the allowable range Wp of alight-receiving position is shifted. For example, as shown in FIG. 4,when the allowable range is shifted from an allowable range WpL,suitable for determination performed when a corrugating flute height ishigh, to an allowable range WpS, the effective line is changed from aneffective line 6L to an effective line 6S accordingly. Thereby, normalor abnormal determination of the flute height with a low corrugatingflute height can be performed. Further, by adjusting the length orposition of the allowable range Wp, the length and position of theeffective line can be changed slightly, so the inspection accuracy canbe finely adjusted.

Here, though shifting the allowable range Wp can be performed byshifting, by input from the outside, the upper limit and the lower limitbeing compared with a light-receiving position by the normal or abnormaldetermining means 71, detector 1 of the present embodiment can utilizeinformation owned by production management device 90 of the corrugatorto shift the allowable range Wp automatically. The production managementdevice 90 of the present embodiment includes production managementinformation 81 comprising various information such as types ofcorrugated cardboard sheets to be manufactured (single-faced corrugatedcardboard, double-faced corrugated cardboard, double wall corrugatedcardboard, and the like), corrugation types, combinations of a mediumbase paper and a liner to be attached to each other, model numbers ofmedium base papers or liners, basis weight, and manufacturing order in acase of manufacturing plural kinds of corrugated cardboard sheets.

In the present embodiment, when a manufacturing condition of acorrugated cardboard sheet is changed such as a case of changing acorrugation type, or a case of changing kinds of a medium base paper anda liner or a combination thereof even if the corrugation type is thesame, production management information 81 is sent from productionmanagement device 90 to computer 60 of detector 1. On the side ofdetector 1, information acquiring means 72 acquires productionmanagement information 81 sent from production management device 90, andextracts flute type information 82 associated with the flute height fromproduction management information 81 including various information.

Next, allowable range shifting means 73 reads allowable range data 86associated with the flute type information 82 extracted by informationacquiring means 72 from allowable range database 85 stored in storingmeans 75. Then, based upon read allowable range data 86, the upper limitand the lower limit which are standards for comparison with alight-receiving position by the normal or abnormal determining means 71are shifted by allowable range shifting means 73, and the allowablerange Wp of the light-receiving position is shifted.

As described above, according to the detector 1 of the presentembodiment, without requiring such complex adjustment as changing theangle of the inspection light 5, the height of the optical projector 2,or the position of the optical receiver 4, whether the heights ofcorrugated cardboard flutes with different corrugation types are normalor not can be determined by the same detector 1, and the detectionaccuracy can be easily adjusted.

Further, by shifting the allowable range Wp of a light-receivingposition, the allowable range Wh of the flute height can be shifted.Therefore, even during operation of the manufacturing line, theallowable range Wp and thus the allowable range Wh of the flute heightserving as the standard for defect detection can be changed easily andrapidly.

In addition, by utilizing information owned by the production managementdevice 90, a proper allowable range Wp (and thus allowable range Wh)corresponding to the type, thickness, or the like of a medium base paperor a liner to be used actually in the manufacturing line can be set.Therefore, whether a flute height is normal or abnormal can bedetermined in appropriately corresponding to flute heights slightlydifferent according to a type, a thickness, or the like of the mediumbase paper or the liner even if corrugation types are the same.

Hereinbefore, though the present invention has been explained through apreferred embodiment, the present invention is not necessarily limitedto the above embodiment, and as described below, without departing fromthe gist of the present invention, various modifications and designchange are possible.

For example, in the above embodiment, the case has been illustrated inwhich the direction in which the inspection light is projected from theoptical projector is opposite to the traveling direction of flutes, butthe present invention is not limited thereto, so the inspection lightmay be projected in the same direction as the traveling direction offlutes.

Further, the case in which the computer of the detector passivelyreceives the production management information sent from the productionmanagement device has been illustrated, but the present invention is notlimited thereto, so it is possible to perform setting in which a signalrequiring transmission of information is sent to the productionmanagement device from the defect detector.

Further, though the case of using a PSD element as a light-receivingelement has been illustrated, the present invention is not limitedthereto, so a photodiode array or an image sensor can also be used.Further, though a case of disposing plural pairs of a light-emittingelement and a light-receiving element in the width direction of acorrugated cardboard sheet is illustrated, the present invention is notlimited thereto, so, for example, it is also possible to adopt aconfiguration in which the light-receiving element is two-dimensionalimage sensor, and reflected light can be received over almost full widthof a corrugated cardboard sheet by one image sensor.

1. A defect detector for corrugated cardboard flutes including anoptical projector which projects, to traveling flutes, an inspectionlight having an effective line of which the length is about one pitch offlutes inclined slightly so that a tip of a normal flute mountain ispositioned on or slightly under the posterior end of the effective lineand simultaneously a slope of an adjacent normal flute mountain ispositioned on the anterior end side of the effective line, anddetermining whether the height of a flute is normal or abnormal basedupon the inspection light reflected by a flute mountain, comprising Anoptical receiver equipped with a light-receiving element for receivingthe inspection light reflected by a flute mountain to output informationcorresponding to the light-receiving position, A normal or abnormaldetermining means for, if the light-receiving position detected from theinformation output by the light-receiving element is within an allowablerange Wp, determining that the height of the flute is “normal”, i.e. theheight of the flute is within the allowable range Wh, and, if thelight-receiving position is out of the allowable range Wp, determiningthat the height of the flute is “abnormal”, i.e. the height of a fluteis out of the allowable range Wh, and An allowable range shifting meansfor shifting the allowable range Wp of the light-receiving position toadjust the allowable range Wh of the flute height depending on acorrugation type of being corrugated cardboard flutes.
 2. The defectdetector for corrugated cardboard flutes according to claim 1,comprising a storage device which has stored an allowable range databaseassociating flute type information including corrugation typeinformation, medium information, and liner information with allowablerange data, and information acquiring means which acquires the flutetype information from a production management device of the corrugator,wherein the allowable range shifting means which reads, from theallowable range database, the allowable range data associated with theflute type information acquired by the information acquiring means toshift the allowable range so as to conform the allowable range to theread allowable range data.